<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<style type="text/css">
			/*后代选择器*/
			.a .son{
				background-color: red;
			}
		</style>
	</head>
	<body>
		<div class="a">
			<div class="son">111111111</div>
		</div>
		
		<div class="b">
			<div class="son">222222222</div>
		</div>
		
		<div class="c">
			<div>
				<div class="son">333333333</div>
			</div>
		</div>
	</body>
</html>